The field of the invention relates to processes for the production of aromatic acids, and in particular, to an improved aromatic acid manufacturing process that recovers lost product, heavy metal oxidation catalyst and process water used in the manufacture of certain aromatic acids. The aromatic acids include, but are not limited to, terephthalic (TA) and isophthalic acids (IPA).
Very large amounts of aromatic acids are produced worldwide each year. The major aromatic acids produced are TA and IPA that are raw materials for textile fibers and food packaging resins and films. The typical aromatic acid is produced from the oxidation, in the presence of a heavy metal oxidation catalyst, of alkyl aromatics such as paraxylene and metaxylene to the corresponding aromatic acid. The oxidation process produces a technical grade product typically not suitable for certain applications because of impurities produced during the oxidation process. The impurities are usually partially oxidized intermediates (paratoluic acid, 4-carboxybenzaldehyde, etc.) and color formers such as 2,6-dicarboxyfluorenone. The impurities create deleterious effects on polymer products produced from the technical grade aromatic acid.
Technical grade TA and IPA are further purified to remove the impurities by dissolving the aromatic acid in very hot demineralized water at elevated temperature and pressure. The aqueous solution and hydrogen is then passed through a vessel containing a hydrogenation catalyst that purifies the aromatic acid product further. The aqueous solution is then cooled causing the aromatic acid to crystallize out of solution. The aromatic acid is then recovered by conventional means such as centrifugation or rotary vacuum filtration. The hydrogenated impurities remained dissolved in the wastewater. The wastewater generated from the process contains the unwanted impurities as well as residual amounts of the aromatic acid and the heavy metal oxidation catalyst. Typically the wastewater is sent to a wastewater treatment process resulting in the loss of the aromatic acid product, heavy metal oxidation catalyst and water.
Dickerson et al. (U.S. Pat. No. 4,540,493) disclose a process for treating wash water from the manufacturing of terephthalic acid. The process includes the steps of passing the wash water through a filter medium to remove undissolved terephthalic acid solids, passing the filtered water through a cation exchange resin in hydrogen form to remove the metal catalysts, and passing the water through an anion exchange resin to remove dissolved terephthalic acid and dissolved organic acid byproducts. However, this process has the disadvantage that the use of cation IER in the hydrogen form can result in the fouling of the resin since the hydrogen ion could react with the soluble aromatic acids and cause them to precipitate and foul the resin. The anion resin also consumes considerable amounts of sodium hydroxide to remove the aromatic acids. Also this process does not directly recover for reuse the cobalt/manganese catalyst. It is desirable to recover all components of the wash water for recycling.
Accordingly, there exists a need for the efficient recovery of the aromatic acid product, heavy metal oxidation catalyst, and the wash water.